Not Applicable
Not Applicable
Not Applicable
This invention relates to polyolefin blends which have superior scratch resistance along with rigidity and impact toughness. The invention also relates to shaped articles made from these blends as well as methods for producing such articles.
In numerous applications, such as many in the automotive industry, a polymeric material that exhibits a good level of scratch resistance balanced with rigidity and impact toughness is desired. These properties tend to vary, however, such that efforts to enhance one will often result in deterioration of one, or both, of the others.
Polypropylene blends are useful in a wide variety of applications due to their strength, environmental resistance and processability. While highly crystalline polypropylene does exhibit good mar and scratch resistance, it does not possess the impact toughness required in many important applications such as the making of automobile parts. Special polymeric materials have been developed that overcome this problem to some degree.
Attempts to remedy polypropylene""s deficiency in impact toughness by blending with impact modifying copolymers of ethylene and other xcex1-olefins, terpolymers of ethylene, other xcex1-olefins, and dienes have not been completely successful. Elastomer modified polypropylene blends, also known as thermoplastic polyolefins (TPO), have the advantage of improved toughness, especially for cold temperature impact. They are widely used for formed or shaped articles such as automotive parts, toys, furniture, and housing products. Although the impact toughness of those compositions is improved by these modifiers, the scratch resistance has been found to decrease. That is, the scratch resistance of polypropylene blends containing impact modifiers such as ethylene-propylene copolymers, ethylene-propylene terpolymers, ethylene-butene copolymers, or ethylene-octene copolymers is poor. Increasing the crystallinity of the polypropylene to obtain a harder surface, and/or adding hard mineral filler to these blends, has been attempted as a countermeasure without complete success.
One conventional method to enhance surface characteristics is to use inorganic particulate material. Uniform dispersion of these particulates is difficult to achieve, however, and this results in non-uniform surface properties in such products. The use of these particulates also tends to damage other desirable physical properties of the polyolefin, resulting in loss of impact strength and/or toughness, and contributes to stress whitening which is not desirable.
Another conventional way to enhance surface characteristics of various articles is to apply acrylic polymers or coatings to an article and subsequently cure the polymer or coating with a radiation source, such as ultraviolet radiation.
A method to enhance surface characteristics of polyolefins is described in U.S. Pat. No. 4,000,216, which discloses an extrudable, moldable, or heat formable blend of a thermoplastic polymer and a surface altering agent of at least one monoethylenically unsaturated monomer for said thermoplastic polymer, wherein the surface altering agent has cross-linked polymer particles having an average size of 1 to 30 microns. The surface altering agent is preferably prepared by an endopolymerization, which is used with a compatible polyolefin to be altered.
Despite these prior art formulations, there remains a need to obtain polymeric materials which have a good level of mar/scratch resistance along with the physical property requirements of rigidity, strength, processability, and low temperature impact toughness.
This invention relates to compositions of thermoplastic polymer blends and formed articles made thereof, which exhibit superior physical properties such as a combination of excellent scratch resistance, rigidity and impact toughness.
The thermoplastic polyolefin blend includes from about 40 percent to about 80 percent of a base component of propylene-containing polymer; from about 5 percent to about 30 percent of a toughening component; and from about 3 percent to about 40 percent of a thermoplastic elastomer, preferably a styrene block copolymer, a random copolymer of styrene and ethylene, or mixtures thereof. A preferred thermoplastic polyolefin blend includes between about 50 percent to about 70 percent of the base component; between about 10 percent to about 20 percent of the toughening component; and between about 5 percent to about 20 percent of the thermoplastic elastomer.
The thermoplastic elastomer is advantageously a high-styrene polymer, containing at least about 50 percent styrene, preferably at least about 60 percent styrene, and more preferably at least about 70 percent styrene. The propylene-containing polymer may be a crystalline or semi-crystalline polypropylene, a copolymer of propylene and another xcex1-olefin, or a mixture thereof. Preferably, the propylene-containing polymer is a crystalline or semi-crystalline homopolymer of polypropylene.
The toughening component may be a copolymer of ethylene and a first xcex1-olefin, for example a copolymer of ethylene and I-octene; a terpolymer of ethylene, a second xcex1-olefin, and/or at least one diene; or a mixture thereof. The first xcex1-olefin, the second xcex1-olefin, or both, are advantageously selected from the group consisting of propene, 1-butene, 1-hexene and 1-octene. The diene is advantageously selected from, for example, 1,4-hexadiene, cyclooctadiene, ethylidene norbornene, dicyclopentadiene, or mixtures thereof.
Examples of styrene block copolymers that are useful in this invention include styrene-(ethylene-butene)-styrene, styrene-(ethylene-propylene)-styrene, styrene-isoprene-styrene, styrene-isoprene, styrene-butadiene, styrene-butadiene-styrene, or mixtures thereof. The quantity of styrene in the block polymer is preferably at least 60 percent by weight of the block polymer.
Advantageously, the thermoplastic polyolefin blend further includes up to about 20 percent of polyethylene. Preferably, the polyethylene is high-density polyethylene and the high-density polyethylene is present in an amount between about 2 percent to about 18 percent, more preferably between about 5 percent to about 15 percent of polyethylene.
The thermoplastic polyolefin composition blend may advantageously also contain a filler in an amount of up to about 30 percent, preferably between about 2 and about 20 percent by weight of the entire composition. The fillers can be inorganic fillers or polymeric fillers such as polystyrene, polyamides, polyesters, polysulfones, polyether sulfones, polyphenylene oxides, or mixtures thereof.
This invention relates to thermoplastic polymer blends and shaped articles made therefrom, which exhibit superior physical properties such as a combination of excellent scratch resistance, rigidity and impact toughness. Such blends contain polyolefin homopolymers and copolymers and copolymers of styrene and xcex1-olefins. The blend of polypropylene and olefins rubber with the addition of styrene copolymers and high-density polyethylene to conventional polyolefin blends enhances the scratch resistance of the substrate surface without sacrificing other physical properties such as rigidity and toughness.